Stabilized chloral



about 9 7 6., while the polymers are solids.

standing at ordinary temperatures; the monomer changes to oneor morepolymeric so lid 'iorms. ,'Ihe problem of polymerization does not oeeur'-if Patented Apr. 25, 1950 Dwight Williams, Charlestom, and Robert M,'Tliomasand George S. Haincs, South Charleston, W. Va;, assignorstoJFoodMachinery and Chemical Corporation, New-York, .N. Y., acorporation-of Delaware No'Drawingf Application February-'21, 11946,,

.Serial No. 650,128

eclaimsr (or. 260-601) This invention relates to stabilized chloralsuit-:able for commercial use.

Chloral is becoming --increasingly important as a commercialorganicchemical where it is used in organic syntheses and asapharmaceutical. agent. Its prominence ,asa commercial chemicalhas beengreatly increased by its being used as an intermediate in the productionof'D; D. T;, namely, 22- bis- ('4 chlorophenyli). I',1 glitric'hiloroethane.

Ghloral (:triehloroacetaldehyde): isa substance exists-in polymericaswell aswmonomeric form. The monomer is aliquid having: a ireezi ngpoint of" about w" (5; and a boiling point cf Upon the-liquid chloral isused when freshly prepared,

' but, from a practical viewpoint; this frequently impossible.Regardless of whether-the chloral is used per se or as anintermediatey-it'is' decidedlydimcult and disadvantageous to use theliquid andsolid form conjointly; Generally speaking,

itis far better to. have the chloral in the liquid fmm, The. polymersmaybe reconverted tothc economical manufacture of D. D.'T. substantiallyfree of objectionable color.

We have found that certain nonaromatic ethers, including aliphatic andcyclic ethers are capable of reducing the tendency of chloral topolymerize approximately 90 per cent without imparting any colorwhatsoever. We haverfound also that aliphatic amines and.'.certain.other nonaromatic compounds containing nitrogen have V the property of.substantially completely inhibiting the. tendency of the monomericchloral to polymerize while imparting, either no color or color ofanintensity which is not-objectionable.

Among the ethers. suitableflfor stabilizing the chloral. arethevariousaliphatic and cyclic ethers, but diethyl ether, diisopropylether, and. loft-dioxane have been found especially .suitable,,ior

- theynot only exert a stabilizing efiecturpon-the chloral bu-t'may bereadilydissolved in the-chloral in aneffective quantity withoutimparting. any color whatsoever to'the chloral: composition. Thealiphatic; amines and. certain other nonaromatic amine compounds exertan even, stronger. inhibitl'iquid monomer by distillation in thepresence of mineral acids or byother costly procedures, which shouldbeavoided. Thus itlisof reatpractical 'importanceto providecommercialchloral in va form which is stable in storage.

Previous attempts to stabilize chloral have been directed--principallytowards stabilizing it against its tendency to undergoautoxiclation in the presence of Some-success has been experiencedingzaction uponthe tendency of the chloral: to

polymerize. Some of these nitrogen compounds impart discernible colortothe chloral; but'the "preferred; compounds can be incorporatedinsettcctive quantities without imparting color of; an objectionableintensity. Among thenitrogen compounds found particularly suitable arethe primary aliphatic amines of L to 18 carbon atoms,

- more particularly the mono-alkyl: amines-c1110 in the;stabilizing-of-chioral, but all of the stabilizers. known in the priorart'have. imparted. color to the chloral of such intensity thatthechloral no longer" suitable for commercial purposes;

' f It is therefore a major purposeof. this:' invention to provide.chloral having its tendencyto;'pol y merize substantially completelyinhibited or greatly retarded iby the incorporation of..a. stabi1- jizing agent without imparting any colorto-the chloral or by impartingcolor which is not of eb- 110x18 carbon atoms, including n-decylamine,n-dodecylamine, n-ztetradecylami'ne, n-hexadecylasnine; andn-octadecylamine. Other suitablte aminenitrogen compounds aremorpholine, certain secondary and: tertiary aliphatic. amines, and.thercycloaliphatic: primary amineicyclohexylamine.

Theioregoing; amines andiethers may The used singlyor as an admixture.In referring" 1702211011- aromatic aminesor-nonaromatic ethers, we meanjectionable intensity. It is a special object of ourinvention to providechloral' which is sufficiently stable-in storage--and duri-ngtransportation: to

permitits-being suppliedtic-manufacturers in-"- a those: amineswandethers' which do not contain an aromatic group attached directly to theamine nitrogen or ether oxygen atom.

Itwi=ll-be= understood that term ether as usecthere-in. is used in theco-nventlonalsehse,

namely. to: encompass" compounds containing-a s mme suitable for" useasany intermediate-in the carbon-oxygen-carbon linkage with only carbon'trol specimens. indicates that only 1 per cent as much polymer orhydrogen attached to the carbon involved in said linkage.

The inhibitors or stabilizers may be incorporated in varying amounts,depending upon their inhibiting action. Generally speaking, percentageswithin the range of 0.05 per cent and 0.25 per cent by volume areadequate, although percentages varying from 0.001 per cent to 1 per centhave beenfound to be practical from an economic standpoint." Certain ofthe ethers have been used in concentrations as high as per cent withoutimparting any undesirable properties to the chloral, but the preferredconcentration of ethers does not usually exceed about 0.25 per cent byvolume.

In evaluating the capacity of the stabilizers to inhibit the tendency ofchloral to polymerize, we found that variations in the specific gravityof the chloral were not always a reliable index of the degree ofpolymerization, for the specific gravity may be increased by theformation of chloral hydrate through the absorption of moisture from theatmosphere. We observed further that turbidity represents a usefulqualitative index of the degree of polymerization, but such an indexdoes not constitute a quantitative evaluation. Knowing that the polymerof chloral is practically insoluble in water while chloral itself issoluble in water, a special procedure was developed for a quantitativedetermination of the amount of polymer present in a monomer compositionwhich had stood over a considerable period of time. The procedureconsisted in adding 10 ml. of chloral to 100 ml. of water, boiling for 2or 3 minutes, filtering, drying the precipitate, and weighing thelatter. The dried precipitate represented the amount of chloral whichhad been converted into the solid polymer. In order to obtain ameasurement of the potency of the various inhibitors, a rating wascalculated by dividing the concentration of the polymer in a testspecimen by the concentration of the polymer in the control specimen andmultiplying this ratio by 100, This device gave a comparison on a,percentage basis of the relative amount of polymer present respectivelyin the test and the con- For instance, a rating of 1.0

was formed in the test specimen as in the control specimen.

In order to determine the amount of color present in the test specimen,both visual observation and photoelectric measures of the light absorbedby a layer of the chloral were used. The photoelectric evaluation wasmade with a 40 mm. layer of chloral, using a 05-47 Wratten filter(blue).

The color index assigned was based upon the perhad no color afterstanding for thirty days.

The tables which follow constitute an evaluation of a number ofcompounds which have been I found suitable for stabilizing chloralagainst poly- ;merization evaluated in accordance with the procedureoutlined above; In several instances, in- I dicated by omissions fromthe table, the photo-- electric evaluation of the intensity of the colorwas not accurately obtainable. In certain instances the inability toaccurately measure the color intensity photoelectrically was due to thefactthat the inhibitor or stabilizer was not com-t pletely soluble inthe chloral.

The comparisons were made by keeping the control and the experimentalsamples in a dark room for thirty days before the degree ofpolymerization of the chloral was evaluated.

Table I .--Ethers Cone, Stability Color, Color Ether Vol. Rating VisualPhoto- Percent elec Diethyl Ether 0.25 11 None 0.0

Diisopropyl Ether.. 0.25 15 do.. 0.0

1,4-Dioxane 0.25 15 -do... 0.0

Ethylene Glycol Mono- 0.25 23 do 0.0

7 methyl Ether.

Control 100 ..do

Table II.--Nztrogen compounds Stabilit c010:

Com ound Vol y Photo- 9 Percent Ratmg vlsual elec.

Ethylene diamina. 0.10 0.5 Yellow. 30

Di-n-propylamine 0.10 4.0 do. 58

Di-n-butylamine 0.10 4.0 do 42 n-Amylarnine 0.10 0.5 do 49 Triamylarnine0.10 3.0 do 42 Cyclohexylaminc 0. 10 0. 9

Mono-n-decylarnine 0. l0 0. 5 20 Monon-clodccylamine. 0. O5 0. 3 l0Mono-n-dodecylaniinc 0. l0 0. 3 48 Mono-n-dodecylamine. 0. 25 0. 3 68Mono'n-tetradecylamine 0. 10 0. 3 l7 Mono-n-hexadecylamine. 0. l0 0. 2lVIono-n-ootadecylamine. 0. 10 0. 6 Morpholine 0. 10 12.0 Control 100tions they are unsatisfactory as stabilizers against polymerization.Apparently in the oxidation tests of the prior art, the chloral waspurified by converting it to methachloral in the presence of sulfuricacid, washing the methachloral, and reconverting the methachloral tochloral by heating. The chloral used in all of our evaluations waspurified by contacting it with sulfuric acid, decanting it therefrom,and distilling it from the decanted mass.

Thefollowing table shows the relative unsuitability of a representativegroup of aromatic compounds for stabilizing chloral againstpolymerization particularly when the intensity of the color imparted istaken into consideration. In

the evaluations the inhibitor was added in a quantity equaling 0.1 percent by volume when the inhibitor was a liquid and in a quantityequaling 0.1 per cent by weight when the inhibitor was a solid.

Table III.-Aromatic compounds Stability Color, Compound Rating VisualPhotoelec.

Phenylene diamine 6 Brown 100 Phenyl-naphthylamine 6 Black. 100o-Aminophenol 8 .do 100 9 .do 100 14 .do 100 14 Yellow 59 Black H 91'Pink 100 Hydro quinone 97 Red 100 Catechol 99 Black 100 I Resorcinol 122Red 100 It will be understood that theforegoing description of ourinvention is illustrative and that modifications, adaptations, andalterations in the made without departing from the scope of ouracteristics of untreated chloral and its tendency 15 to polymerizegreatly retarded comprising chloral containing not more than 1 per centby volume of diethyl ether dissolved therein.

4. A process for stabilizing chloral which comprises adding tocommercially pure chloral not more than 1 per cent by volume of analiphatic ether.

5. A chloral composition comprising chloral having incorporated thereinnot more than 1 per cent by volume of diisopropyl ether.

6 6. A chloral composition comprising chloral having incorporatedtherein not more than 1 per cent by volume of 1,4-dioxane.

DWIGHT WILLIAMS. ROBERT M. THOMAS. GEORGE S. HAINES.

REFERENCES CITED 10 The following references are of record in the fileof this patent:

UNITED STATES PATENTS Number Name Date 1,763,326 Reed June 10, 1930FOREIGN PATENTS Number Country Date 612,396 France July 31, 1926 OTHERREFERENCES Trillat, Bull. Soc. Chim. (Mem.), Ser. 3, vol. 17, pages231-234 (1897).

Meyer et al., Liebigs Annalen, vol. 171, pages

2. A CHLORAL COMPOSITION HAVING ITS COLOR CHARACTERISTICS SUBSTANTIALLYUNCHANGED AND ITS TENDENCY TO POLYMERIZE GREATLY RETARDED COMPRISINGCHLORAL CONTAINING THEREIN NOT MORE THAN 1 PER CENT BY VOLUME OF ANALIPHATIC ETHER.